fix crash when rotating caption dialog

[connyduck]

Steps to reproduce: Open the dialog to set a catption on an image. Rotate the screen.

Stacktrace

Exception java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
  at com.keylesspalace.tusky.components.compose.dialog.CaptionDialog.onCreateView (CaptionDialog.kt:61)
  at androidx.fragment.app.Fragment.performCreateView (Fragment.java:3114)
  at androidx.fragment.app.DialogFragment.performCreateView (DialogFragment.java:775)
  at androidx.fragment.app.FragmentStateManager.createView (FragmentStateManager.java:557)
  at androidx.fragment.app.FragmentStateManager.moveToExpectedState (FragmentStateManager.java:272)
  at androidx.fragment.app.FragmentStore.moveToExpectedState (FragmentStore.java:114)
  at androidx.fragment.app.FragmentManager.moveToState (FragmentManager.java:1455)
  at androidx.fragment.app.FragmentManager.dispatchStateChange (FragmentManager.java:3034)
  at androidx.fragment.app.FragmentManager.dispatchActivityCreated (FragmentManager.java:2952)
  at androidx.fragment.app.FragmentController.dispatchActivityCreated (FragmentController.java:263)
  at androidx.fragment.app.FragmentActivity.onStart (FragmentActivity.java:350)
  at androidx.appcompat.app.AppCompatActivity.onStart (AppCompatActivity.java:251)
  at android.app.Instrumentation.callActivityOnStart (Instrumentation.java:1543)
  at android.app.Activity.performStart (Activity.java:8682)
  at android.app.ActivityThread.handleStartActivity (ActivityThread.java:4219)
  at android.app.servertransaction.TransactionExecutor.performLifecycleSequence (TransactionExecutor.java:221)
  at android.app.servertransaction.TransactionExecutor.cycleToPath (TransactionExecutor.java:201)
  at android.app.servertransaction.TransactionExecutor.executeLifecycleState (TransactionExecutor.java:173)
  at android.app.servertransaction.TransactionExecutor.execute (TransactionExecutor.java:97)
  at android.app.ActivityThread$H.handleMessage (ActivityThread.java:2584)
  at android.os.Handler.dispatchMessage (Handler.java:106)
  at android.os.Looper.loopOnce (Looper.java:226)
  at android.os.Looper.loop (Looper.java:313)
  at android.app.ActivityThread.main (ActivityThread.java:8810)
  at java.lang.reflect.Method.invoke
  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:604)
  at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1067)

Restoring the saved caption after the view was created fixes the problem.